Onychomycosis or tinea unguium (ringworm of the nails) is a chronic disease of the nails due to parasitic fungi. Onychomycosis can cause the nail to appear thickened and lusterless, and often causes nail discomfort. Also, the infected nail harbors a reservoir of pathogenic organisms which can spread to and reinfect other parts of the body, causing chronic diseases such as onychomycosis in other nails, athletes foot, foot dry skin and the like. Onychomycosis is prevalent throughout a large proportion of the population, with most of those afflicted from the ages of 40 years and older. To date, the United States Food and Drug Administration (FDA) has not approved any topical treatments for onychomycosis, either prescription or over-the-counter (OTC), due to the poor response of treatments evaluated. This poor response is partly because the nail is a difficult barrier for anti-fungal compounds to penetrate. In the Federal Register, Tuesday, Mar. 23, 1982, Part III Department of Health and Human Services, Food and Drug Administration, Topical Antifungal Drug Products for Over-the-Counter Human Use, Establishment of a Monograph reports: "Fungal infections of the . . . nails tend to be chronic. They respond poorly to topical therapy, partly because of the thickness of the nails . . . sites of infection provide inaccessible locations for fungi, thus drastically decreasing the penetration of topical antifungals. For this reason, OTC topical antifungals must be labeled that they are not effective for the treatment of ringworm of the . . . nails."
The research by Jacob Brem, "Treating Onychomycosis," The Lancet, Oct. 29, 1977, Vol 2., p 937 demonstrates the extreme measures taken by one researcher to penetrate the nail: ". . . five or six holes are drilled in the nail plate, in the form of a crescent . . . Anaesthesia is not necessary. However, the introduction of the needle is felt when the nail bed is reached . . . The holes are enlarged by dipping a round toothpick in dichloroacetic acid and drilling through the hole in the nail. When the acid reaches the nail bed a burning sensation is felt . . . A week later, five or six new holes are drilled . . . If necessary, more holes could be drilled and further applications of acid could be given."
In a similar manner, the book, "Diseases of the Nail" by V. Pardo-Castello, Thomas Books, Baltimore, Md., (1936), pp. 22-40 describes several treatments for onychomycosis, including the following: "Craik (43) has reported two cases treated with success by means of daily applications of a solution of 4 grams of salicylic acid in 45 c.c. of methylated spirit, after thoroughly scraping the nail. The cited reference, R. Craik, "A Simple Treatment of Ringworm of the Nails", Brit. M. J. Feb. 1920, p. 185 describes a procedure wherein a lotion containing salicylic acid was ". . . to be painted on after scraping [the finger nail] every night, and without scraping every morning, and to be used for three months or longer." Scraping a finger nail each day for three months or more has effect of thinning or completely removing the nail plate.
Avulsion or surgical approaches for treating onychomycosis have also been used. Infected nails are treated by surgically or chemically removing the nail and treating the exposed nailbed with topical antifungals. These treatments must be continued until the nail grows out, typically 6 months or more. Although the surgical approach generally results in cure rates significantly higher than those reported for topical treatments, most patients dislike undergoing surgery, which can result in permanent nail loss.
Clearly, there is a need to provide an effective method for treating onychomycosis in which salicylic acid or a salt, ester or mixture thereof can be applied topically to an afflicted nail, without the need to drill holes in the nail, scrape the nail daily for three months or more and/or avulse the nail. There is also a need to provide a method for treating onychomycosis through use of a medicated device or a film-forming liquid preparation which enables the salicylic acid to remain in contact with the nail, thus facilitating its penetration into the nail.